


i should be so selfish

by parsnipit



Series: flashpoint [1]
Category: Undertale (Video Game)
Genre: Alternate Universe - Underfell (Undertale), Banter, Brief insecurities, Implied Sexual Content, M/M, Overprotective Gaster, Possessive Behavior, Unhealthy Relationships, Violence, no explicit smut but grillby and gaster are definitely some handsy bastards in this
Language: English
Status: Completed
Published: 2019-12-18
Updated: 2019-12-18
Packaged: 2021-02-26 16:55:05
Rating: Mature
Warnings: Creator Chose Not To Use Archive Warnings
Chapters: 1
Words: 2,328
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/21851650
Author URL: https://archiveofourown.org/users/parsnipit/pseuds/parsnipit
Summary: Ninety-nine percent of the time, Gaster isn’t a possessive person. He’s secure in the knowledge that no one would risk taking anything from him, nor presume to so much as brush against his possessions, without his explicit permission. One of the many perks, he supposes, of being the Royal Scientist.The other one percent of the time, he’s at Grillby’s.
Relationships: W. D. Gaster/Grillby
Series: flashpoint [1]
Series URL: https://archiveofourown.org/series/1574302
Kudos: 59





	i should be so selfish

**Author's Note:**

> warnings: possessive behavior, violence, murder, injury, blood, a brief but gross attempt to pressure/guilt someone into sex (not in the main relationship), some nsfw-ish stuff near the end (but nothing explicit)
> 
> written for a prompt by @ninvic-0 on tumblr!

Ninety-nine percent of the time, Gaster isn’t a possessive person. This is, perhaps, because what is his is  _ his,  _ and no one dares question that. There is no reason, therefore, to feel any sort of possessiveness—he feels only a calm, benign sense of ownership when he looks upon his property or his work. A sort of  _ oh, that’s mine,  _ and a sense of quiet pride. He’s secure in the knowledge that no one would risk taking anything from him, nor presume to so much as brush against his possessions, without his explicit permission. One of the many perks, he supposes, of being the Royal Scientist.

The other one percent of the time, he’s at Grillby’s. 

He  _ hates  _ going to Grillby’s. Oh, he likes Grillby well enough (as well as he likes any of his possessions—more so than most, even), but the  _ bar— _ agh. It’s a loathsome place. There’s too much noise, too much light, too many bodies, and it  _ reeks  _ of alcohol and sweat and smoke. What’s more, everything that happens there is very out of his control, which is not something he prefers. In fact, the very thought of it puts a distasteful grimace on his face. 

Most of the time, Grillby comes to visit Gaster, in  _ Gaster’s  _ territory, on  _ Gaster’s  _ terms, and that’s just the way Gaster likes it. Today, however, the elemental had been...stubborn. Gaster could have refused to visit him at all, of course, but he finds that thought even more distasteful than the thought of visiting the bar. He...misses Grillby, he supposes. It’s been quite some time since they’ve seen each other. There is also an unfortunate side effect of relationships called  _ compromise,  _ and even Gaster himself isn’t immune to it. 

So here he is, dragging himself through the dreaded cold of Snowdin to visit that damned bar. Belous stops him at the door, her eyes narrowed and fur bristling, until she recognizes him. “Dr. Gaster,” she says, a flicker of surprise crossing her face. She covers it quickly, her expression smoothing back into something professional and crisp. “Go right in. Please enjoy yourself.”

“Oh, somehow I doubt it,” he says, sour, as he trudges into the bar. He is immediately overwhelmed by light and noise and the jostle of too many bodies, too many, too many,  _ too many— _

He grinds his teeth, digs his elbow into one unlucky fellow’s kidney, and shoves his way through. A few people dare to snap at him when they feel him move by, but they quickly startle away when they realize who they’re looking at. They don’t look for long, their eyes skittering away from him, as though to look for more than few seconds will condemn them. Perhaps it will. Gaster isn’t in a very pleasant  _ mood.  _ Aforementioned mood does brighten, some, upon seeing a flicker of glowing purple—Grillby, the one and only reason for this miserable excursion. He’d best make it worth Gaster’s while. (He usually does; Gaster wouldn’t be here otherwise. He’s hardly that selfless.) 

...then he sees the vampire.

They’re draped across the bar, a glass of wine-dark blood in one hand. Their other hand is lifted, delicate fingers curled through the thin golden chain around Grillby’s neck. Even as Gaster watches, they tug the chain, and Grillby stoops for them, brings their faces level. Gaster freezes in his tracks—horribly, awfully,  _ sickeningly  _ out of control. 

“What do you say, hm?” the vampire purrs, moving to cup Grillby’s face in one palm. They twirl a finger through his flames, and Gaster’s own fingers curl into fists. “As soon as you close, we can take a little trip to the back room, and I’ll let you get me nice and heated.”

“Mm, I wouldn’t risk it, if I were you,” Grillby says, his voice a low rumble. That voice would usually have Gaster shivering in delight, leaning forward for a fight or a kiss or both. Probably both. Right now, however, it just makes him feel cold.

“Oh, because you’re such a big, bad monster, is that right?” the vampire asks, a grin flitting across their mouth. “Don’t worry. I’m not as fragile as I look. You won’t burn me, sweetheart, although I would  _ love _ to see you try.”

“Afraid it’s not me you’d need to be scared of.” Grillby props his chin in his hand, tugging his chain necklace away from her. “I’m taken, and in no mood to be anything but.”

Gaster...begins to thaw. 

“You?” The vampire laughs, sitting back and flashing their fangs. “C’mon, Grillbz, you can’t be serious. You’re the Underground’s biggest whore—a sleazy guy like you doesn’t just get  _ taken.  _ I mean, that hot bod of yours, babe, that’s public property at this point. Who’d be selfish enough to keep it all to themselves?”

Grillby’s flames dim momentarily, and Gaster’s thawing quickly turns into searing rage. There is a reason he doesn’t do emotions _ — _ because he can’t  _ control  _ them. He can’t control  _ anything  _ when he’s this  _ fucking furious.  _ His anger boils against the backs of his ribs, and his eyelights shrink to mere red slits in his sockets.

“I,” he says, finally stepping to the bar, “would be so selfish.”

Grillby jerks backwards, guilt flashing across his face in freckles of yellow sparks. “Dings! How long have you been here?”

“Long enough,” Gaster says, his voice cold. 

“Ah, shit shit shit shit—hey, but it’s okay, she didn’t mean anything by it. She was just kidding around,” Grillby says, leaning towards him. He lowers his voice. “Let’s not do anything rash. Let’s  _ not destroy my fucking bar again.” _

“You?” the vampire asks, arching one elegant eyebrow. “You’re Grillbz’s new toy? Don’t you think it’s kind of mean, keeping him all to yourself like that?” She leans forward, swinging her legs off of the bar stool. “Would you be interested in sharing?”

Grillby whirls around to face her again, his own voice dropping into something cold and rough. “That’s enough. If you’re interested in leaving here with your life, you’ll get up and go without another word.”

“What?” The vampire laughs, sweeping her hair out of her eyes. “I’m fireproof, babe. I already told you— _ you’re  _ not going to hurt me, and this little guy?” She coos at Gaster, and his bones begin to rattle with rage. “He doesn’t look like he could hurt a fly.”

Gaster lunges. The vampire darts away from him, light on her feet and exactly what he had expected—but he’d gotten her away from Grillby. Once he’s done that, he’s free to do whatever the fuck he pleases. He lashes out with his magic, and her soul pings blue. Surprise flickers across her face (not many monsters are strong enough to use blue magic, and oh, how drastically she’s underestimated him). He flings her outside of the bar with a flick of his wrist, because dear Grillby does cherish this awful place so. 

Outside, his blaster waits. He hears the whine of its blast building, and then an awful shriek as its aim strikes true—but the vampire wasn’t lying. She is, indeed, fireproof. When the gaudy red light of the blast outside fades, he waltzes out of the bar. Belous glowers at him. 

“That is not,” she says, “what I meant by  _ enjoy yourself,  _ Doctor.”

“Pity,” he says. “I’m really starting to.”

His blaster screams with rage as it realizes its prey is still moving, and he flicks a hand at it in a quick sign— _ go free.  _ It takes his command enthusiastically, surging forward with its jaws open. The vampire springs away from it, her eyes blazing. Gaster tightens his grip on her soul, rooting her in place. She still manages to wrest herself from his grip, but not quickly enough. The blaster’s jaws lock onto her arm, and he hears a most satisfying  _ crunch  _ as bone splinters beneath its teeth.

_ Good,  _ he signs to his blaster, and its tail begins to wag vigorously.  _ Bring. _

The blaster deposits the vampire at his feet like a roll of soggy newspaper, and he crouches next to her. She goes rigid, ready to spring away from him, so he brings the full brunt of his magic to bear on her soul again, flattening her to the ground. “Listen,” he says, cocking his head. “Grillby belongs to me now, and no, I’m not interested in sharing. Perhaps if you had asked nicely, we could have had a civil conversation about this, but—”

He stands, rolling his jaw back into its second hinge so he can show her both rows of wicked teeth in a death-grin. “I’m afraid I can’t have a civil conversation with someone who insinuates that Grillby’s body belongs to anyone but  _ himself.  _ If he chooses to whore himself out, so fucking be it, but you’re  _ not to push him into it.  _ How disrespectful can you be? You come into his home, into his place of work, and you do  _ this?”  _ He tsks. “Even for a monster, that’s low.”

“I was just  _ asking,”  _ she spits. 

“And he told you  _ no.  _ What right did you have to keep pushing? To lay any kind of claim on him?  _ Public property,”  _ he hisses, affronted. “Public fucking property.”

“It’s what he  _ is.  _ He’s been a whore for as long as anyone in this damned town can remember, and you think you have any right to change that?”

_ “I  _ didn’t change  _ shit,”  _ Gaster says. “He chose me, and I quite like it that way. It really gets me  _ rattled  _ when dumb fucks like you start rubbing your filthy little hands all over him. But I suppose I can live with it—after all, we both know what he is.” Gaster straightens up, sliding his hands into the pockets of his coat. He curls his blue magic around the vampire’s neck, then twists, sharp and abrupt. Her vertebrae snap, and his blaster whuffs at her dust in excitement. “Heee’s mine now.”

“Really?” Grillby complains, leaning in the bar doorway with a hoard of curious monsters behind him. “Right in front of my bar, really?”

“At least it wasn’t  _ in  _ your bar this time,” Gaster says, shrugging. 

Grillby drags his hands down his face. Then he takes a deep breath and turns to the other monsters, his voice dropping into that brisk, commanding tone Gaster does love to hear: “Alright, we’re closed for the night. Everybody get your shit and get out.”

The crowd is quick to do as their commander bids them. As monsters stream out of the bar, Gaster prowls his way inside again. Mm. This place is much, much better when everyone is gone, and it’s just him and his boyfriend and the low purple lights. Maybe he should murder patrons more often. He takes a seat on the bar, crossing his legs and surveying the dance floor as the last of the monsters trickle their way into the snow. Grillby shuts the door behind them, clicking the lock into place.

Then he whirls around to face Gaster, his flames flaring hotter. “You.”

“Me.” Gaster slides off of the bar, heading for Grillby. As soon as he reaches him, he winds his arms around Grillby’s shoulders and curls his fingers into the golden chain around his neck. “Your knight in shining armor.”

“You made a scene. Again.”

“You invited me here. Again.”

“Why can’t you just behave for  _ once—” _

“I’m perfectly well-behaved when we’re not in this shithole with strangers crawling all over you like fucking fleas, mongrel,” Gaster says scathingly, pulling the chain tight. Grillby growls low in his chest, so Gaster sighs and lets it fall slack again. “Besides, I wasn’t going to just sit back and let her insult you like that.”

“Well, she was only stating the truth, wasn’t she?” Grillby asks grimly, his eyes flickering away.

Gaster leans up, sinks his teeth into Grillby’s throat, and  _ bites.  _ Grillby snarls, his hands coming up to brace against Gaster’s shoulders—but he doesn’t push him away, so Gaster stays put, manifesting a tongue for the sole purpose of laving it through Grillby’s flames. “The truth? Fuck off with that, spark,” he says, spreading his hands over Grillby’s chest to feel it hitch. “Sure, you were a whore, and yeah, you’re pretty much the sleaziest person I know, but that doesn’t make you  _ public property,  _ and I’ll kill anyone who says otherwise—yourself included, so you best watch your mouth.”

“How romantic,” Grillby says, wry. Gaster moves up to mouth at the corner of his jaw, and he sighs heavily, smoke curling from his mouth. “Gods, I don’t know how to control you.”

“That makes two of us,” Gaster mumbles through a mouthful of flame.

“...thanks, though. For—standing up for me.”

“Mm, of course.” Gaster clicks his teeth against the bridge of Grillby’s nose. “You’re  _ mine,  _ after all—and I take good care of what belongs to me.”

“That you do.” Grillby loops his arms around Gaster’s hips, hitching him closer. He bows his head, grazing his mouth across the vertebrae of Gaster’s neck. His flames tickle, and Gaster’s breath hitches, his fingers flexing against Grillby’s shoulders. “Perhaps I should reward your diligence, little bastard.”

“Well, I wouldn’t say no to that,” Gaster purrs, burrowing closer to him. He wedges a knee between Grillby’s legs and savors the full-bodied shiver that runs through him. “What did you have in mind, exactly?”

Grillby moves to nibble at Gaster’s collarbones, hands sliding up and beneath his shirt to glide warm fingers across his ribs. Gaster preens under the attention, arching into Grillby’s hands and grinding his knee up just to hear Grillby choke back a groan. Grillby bites his collarbone in rebuke for that, sharp and swift and demanding. “Mm—I could think of quite a few things, actually.”

“How exciting.” Gaster combs the fingers of one hand through the flames at the back of Grillby’s neck, sliding the other hand down the elemental’s abdomen. “Where shall we start…?”


End file.
